The invention relates to the field of power-steering devices.
More specifically, the invention concerns a method for controlling a power-steering device for a motor vehicle equipped with a stop & start system, the power-steering device including an electric pump unit having at least one electric motor and one processor.
An electrohydraulic power-steering device for a motor vehicle is known from the patent application published under number FR 2 864 000. This device includes an electric pump unit (GEP) incorporating four components that are assembled together such that the pump is driven in rotation by the electric motor under the control of the processor as a function of a signal representing the speed of the vehicle and a signal representing the speed of variation of the angle of the steering wheel. More specifically, when the steering wheel is actuated, the load of the electric motor increases and, as a function of this load increase, the current draw also increases. If the driver of the vehicle is not actuating the steering wheel, the electric motor turns with no load at an idling speed, which varies as a function of the speed of the vehicle. Following actuation of the steering wheel, and therefore a request for power steering, the electric motor turns at a suitable power-steering speed that varies as a function of the speed of the vehicle and the speed of the variation of the current of the motor. When the system determines that power steering is no longer being requested, the motor returns to its initial idling speed. In this device, the signal representing the speed of variation of the angle of the steering wheel is generated by the processor as a function of the current drawn by the electric motor.
This enables power-steering requests to be detected without the need for a steering wheel angle sensor.
A method for controlling an electric pump unit of an electrohydraulic power-steering device for a motor vehicle is also known from the patent application published under number FR 2 907 411. The processor is supplied by an electricity connector and a signal connector that sends the electrical signals required to determine the state of the vehicle. This latter is more specifically defined by the following parameters: the speed of the vehicle, the rotation speed of the steering wheel, the angle of the steering wheel, an automatic performance check and the state of the heat engine of the vehicle. The method involves controlling the electric motor for one or more successive periods not just as a function of respective predetermined values for the aforementioned parameters, but also as a function of a predetermined value of the current drawn by the electric motor of the power-steering device, this current being measured by the processor. This enables the electric pump unit to continue working at least temporarily if the signal connector is disconnected.
Furthermore, a system known as a stop & start system for stopping the heat engine of a vehicle under certain predetermined stopping conditions, then restarting the heat engine under predetermined restarting conditions is known. This system is intended to reduce the gasoline consumption of the vehicle and to reduce the exhaust gas emissions thereof, in particular for urban driving.
In a vehicle equipped with both a stop & start system and a power-steering device, it appears necessary to provide for the correlated control of these two devices. For example, the power-steering device is simply deactivated when the heat engine is in automatic stop mode.
In this regard, the patent application published under number DE 100 50 377 teaches a power-steering device for a motor vehicle equipped with a stop & start system. This device is intended to prevent sudden variations in the power steering force, when the engine is automatically stopped or restarted. To do so, the supply current of the electric motor of the power-steering device is adjusted as a function of the mode in which the motor is running, which may be a normal operating mode, an automatic stopping mode and an automatic restarting mode. If it is determined that the engine is in the automatic stopping mode, the current supplying the electric motor of the power-steering device is progressively eliminated according to a first predetermined behavior law. If it is determined that the engine is in automatic restarting mode, the current powering the electric motor of the power-steering device is progressively increased according to a second predetermined behavior law. If it is determined that the engine is in the normal control mode thereof, the power-steering device is adjusted in the normal way.